Patent GB-574694-A (GB)
Title: Process for producing branched chain paraffin hydrocarbons
IPC: C07C4/10
Filed: 1943-11-17
Abstract: Branched chain paraffins containing at least 5 carbon atoms are produced by demethylating a branched chain paraffin or olefin of at least 6 carbon atoms in the presence of hydrogen and a hydrogenating catalyst at a temperature substantially precluding the splitting off of radicals containing more than 1 carbon atom. The initial hydrocarbon may have one or more tertiary or quaternary carbon atoms or both.  Methyl groups are selectively removed usually from the longest and least branched alkyl group attached to a quaternary or tertiary carbon atom.  Thus, neohexane yields mainly neopentane, isohexane yields isopentane, 2,2,4-trimethyl pentane gives 2,2-dimethyl butane (neohexane), and 2,2-dimethyl pentane (neoheptane), and 2,3,4-trimethyl pentane gives 2,3-dimethyl pentane and 2,3-dimethyl butane. Aliphatic hydrocarbons containing a triptyl group, i.e. having a quaternary carbon adjacent to a tertiary or a group convertible thereto by removal of a methyl or other alkyl group, yield on demethylation paraffins also having such a group. Thus, 2,2,3-trimethyl pentane yields triptane with only small amounts of dimethyl pentanes.  2,3,3-Trimethyl pentane and other hydrocarbons, for example highly branched monanes and decanes, may also be demethylated to triptane.  Hydrogen is consumed in substantially equimolecular proportion to the methane formed apart from any required for saturation of olefinic linkages. Preferred catalysts contain iron group metals or oxides, alone or on refractory carriers.  A catalyst containing 66 per cent total nickel, 30 per cent diatomaceous earth, and 4 per cent oxygen as nickel oxide or an analogous cobalt catalyst is suitable.  They may be used powdered or pelleted.  Other catalysts are platinum and palladium, and oxides and sulphides of metals in the left-hand columns of Groups 5 and 6. Temperatures range from about 175-375 DEG  C. at pressures of 1-300 atmos., the higher pressures generally requiring higher temperatures. A lowering of the partial hydrogen pressure generally necessitates a lowering of temperature for the same conversion.  The hydrogen may be admixed with inert gas such as methane which may be recycled with the hydrogen separated from the products.  Batch or continuous operation may be used, for example of the fluidized fixed bed type.  The products, after catalyst separation if necessary, are fractionated and unconverted hydrocarbon recycled.  In examples: (1) neohexane and hydrogen are passed over the above described nickel catalyst at temperatures ranging from 215-253 DEG  C. with a neohexane charging rate of 0.57 or 1.2 vols./vol./hr. to yield mainly neopentane; (2) 2,2,3- with some 2,2,4-and 2,3,4-trimethyl pentanes are autoclaved with hydrogen at 300 DEG  C. and the same catalyst giving mainly triptane; (3) 2,3,4-trimethyl pentane yields 2,3-dimethyl pentane and some 2,3-dimethyl butane at 240 DEG  C. and 13.6 atmos.; (4) 2-methyl pentane is autoclaved at 250 DEG  C. giving mainly isopentane; (5) to (8) mixtures of 70 per cent 2,2,3-trimethyl pentane and 30 per cent of the 2,3,4-isomer are autoclaved at temperatures from 280-320 DEG C. yielding mainly triptane; (9)-(13) 60 : 40 mixtures of the same octanes are passed continuously through the same catalyst at varying temperatures, pressures, space velocities and molar ratios of hydrogen to hydrocarbon to yield principally triptane.